1. Field of the Invention
The present invention relates to a screwdriver bit, especially to a screwdriver bit that reduces torsion force and has a strengthened structure.
2. Description of the Prior Art(s)
With reference to FIG. 3, a conventional screwdriver bit comprises a handle 90 and a head 91. The handle 90 has a shank 92, a connecting portion 93, a necking surface 94 and an annular shear groove 95. The connecting portion 93 has a distal end and a cross-sectional diameter being shorter than a cross-sectional diameter of the shank 92. The necking surface 94 is formed around and between the shank 92 and the connecting portion 93. The annular shear groove 95 is formed around and between the necking surface 94 and the connecting portion 93. The head 91 is disposed on the distal end of the connecting portion 93.
A power tool or a hand tool clamps the shank 92 and drives the conventional screwdriver bit to rotate. When the screwdriver bit rotates, a torsion force is applied to the handle 90 and twists the connecting portion 93. Thus, a shear force is concentrated on and around the annular shear groove 95 and a shear plane is formed at where the annular shear groove 95 is surrounded. Consequently, the conventional screwdriver bit is twisted off easily on the annular shear groove 95 and has poor durability.
To overcome the shortcomings, the present invention provides a screwdriver bit to mitigate or obviate the aforementioned problems.